Depending on the situation/installation sometimes you can take a hose off and pressurise the tank by blowing into it with your mouth, just sometimes you may spot a chafe, gasket
, hose or screw that bleeds some moisture.
dye and the talc are good indicators as well.
It will only leak to the level of the offending hole, has the leak therefore stopped at a designated height.?
Also most things go wrong after the most recent tampering. Have you recently done any work on the water supply? ie Filter change, hose clamp tightening?
Taste the water is it definately fresh?